The present invention relates generally to the field of waste management, and in particular to a method for treating ammonia-containing organic waste, including but not limited to animal manures. Embodiments of the present invention can be applied to destroy pathogens, reduce noxious odors, and immobilize water-soluble pollutants in such organic waste, rendering the treated waste material safe for storage and application to land as, for example, a fertilizer, liming agent or soil amendment.
Since ancient times, animal manures were recycled back to the land that provided the animal feed, thereby completing the nutrient cycle. As animal production became intensified, the cycle was broken, with chemical fertilizers increasingly used to produce animal feed and the animal manure accumulating at the point of production as an unwanted waste. In many parts of the U.S., Europe and other countries, manure production at large, confined animal feeding operations (CAFOs), primarily poultry, swine, dairy and beef, has resulted in odor, nutrient runoff and pathogen food-chain contamination problems. Until the present, little attention has been placed on the processing of animal manure to address these problems, with most attention being placed on so-called xe2x80x9cbest management practicesxe2x80x9d to contain the manure and ensure that it is applied at agronomic rates. Because of the large concentrations of animal manures at CAFOs, generally well in excess of local needs, the need has arisen to treat manures so that they can be easily stored without causing odor or nutrient leaching problems, to greatly reduce pathogen levels and protect against food-chain contamination, and to create products that have a wide range of utility as fertilizers and soil amendments.
A wide range of technologies were developed to treat wastewater residuals and sewage sludges for pathogen destruction and odor control in response to the large public works expenditures for wastewater treatment in the U.S. in the 1960s and 1970s. Prominent among these were technologies that used alkaline reagents to destroy pathogens, to reduce odors, and to solidify and granulate dewatered sewage sludges to make products that could be used beneficially. The standards that these technologies had to meet were the U.S. EPA regulations for pathogen reductions (see 40 C.F.R. xc2xa7xc2xa7257, 503) and vector attractions (40 C.F.R. xc2xa7503).
A traditional approach to alkaline stabilization of sewage sludges has been the use of lime (CaO) to raise pH to around 12 or to produce heat by exothermic hydrolysis. Alternative technological approaches have involved the use of less expensive alkaline mineral by-products. Patents exemplifying such approaches include U.S. Pat. No. 4,554,002 to Nicholson; U.S. Pat. No. 4,781,842 to Nicholson; U.S. Pat. No. 4,902,431 to Nicholson et al.; and U.S. Pat. No. 5,277,826 to Burns et al. Such patents teach the use of a range of alkaline materials to raise pH to around 12 and to increase total solids as a means of destroying pathogens.
In addition, the use of ammonia to kill pathogens in sewage sludge is disclosed in U.S. Pat. No. 4,793,927 to Meehan et al. Meehan describes the addition of ammonia-containing compounds to sewage sludge as an agent to destroy bacterial, parasitic and viral pathogens within the sludge matrix. U.S. Pat. No. 5,143,481 to Schumacher et al. shows how fluidized bed combustion residue (FBCR), or fly ash, containing CaO can be used to treat sewage sludges by producing heat in an exothermic reaction. U.S. Pat. No. 5,679,262 to Girovich et al. describes the use of mineral by-products to reduce the use of CaO in order to kill pathogens and achieve a dry product. Finally, U.S. Pat. No. 5,417,861 to Burnham teaches how a combination of surviving microflora, salt levels and solids content can provide long-term stability to bioorganic or wastewater sludges.
Despite these extensive efforts directed at the treatment of wastewater and sewage sludge, no comparable technologies have been developed for the treatment of ammonia-containing organic waste such as animal manures. Manure treatment, for example, has historically included only aerobic and anaerobic digestion of liquid manures, while some beef and poultry manure is composed (see D. L. Day and T. L. Funk, Processing Manure: Physical, Chemical, and Biological Treatment (1998) (published in J. L. Hatfield and B. A. Stewart, Animal Waste Utilization: Effective Use of Manure as a Soil Resource (Ann Arbor Press 1998)). The only significant known approach to chemical stabilization of manure is the addition of calcium, iron or aluminum salts to poultry manure to reduce ammonia emissions and to immobilize soluble phosphorus (see P. A. Moore, Jr. et al. and D. M. Miller, Reducing Phosphorus Solubility in Poultry Manure with Aluminum, Calcium and Iron Amendments, J. Environ. Qual., vol. 23, 325-330 (1994)); and U.S. Pat. No. 3,877,920 to Carlberg, which taught the use of fly ash to deodorize animal manures. None of these approaches, however, deal with chemical treatment of animal manure for pathogen destruction.
With respect to pathogen destruction in animal manures, M. B. Jenkins et al., Inactivation of Cryptosporidium parvum Oocysts by Ammonia, Appl. and Env. Microbiol., Vol. 64, 784-788 (1998), shows that free ammonia-containing solutions can destroy Cryptosporidium parvum oocysts in liquid media and suggests that ammonia in manures might be used to kill oocycsts of this organism, but this reference only discusses the use of free ammonia in solution. Large-scale introduction of aqueous ammonia to animal manures presents a host of practical problems, including, but not limited to, problems associated with the handling of large quantities of a potentially-hazardous liquid. The introduction of liquids to manure is counterproductive because manures are inherently wet and need to be dewatered for effective handling and storage. Moreover, aqueous ammonia is caustic, relatively expensive and difficult to handle.
Another problem with respect to the treatment of manures, especially where the treated material is to be used as a soil amendment, relates to the high levels of water-soluble phosphorous and water-soluble trace elements that are often found in such waste material. For example, the application of manure to land in amounts optimal to satisfy nitrogen requirements for crops can result in a buildup of water-soluble phosphorous in the soil, since crop demands for phosphorous are generally much lower than those for nitrogen. This can lead to undesirable runoff of phosphorous during rainfall events and eutrophication of surface waters like lakes, streams and impoundments. Similarly, high levels of water-soluble trace elements, such as copper and zinc, can be phytotoxic to crops, particularly for acidic soils.
In view of the foregoing, it is apparent that there is a need for safe, effective and economical methods for disinfecting and deodorizing animal manures and other organic wastes that takes advantage of the inherent endogenous ammonia in such waste materials. Moreover, in order to avoid environmental problems often associated with land application of manures, it is desirable that such methods limit the level of water-soluble phosphorous, copper and zinc in the end product.
The present invention is directed to methods for disinfecting and deodorizing animal manures and other organic wastes containing ammonia, while also reducing the levels of water-soluble pollutants such as phosphorous, copper and zinc. In accordance with a particular embodiment, the solids content of a sample of animal manure is raised to an approximate minimum of 30% so as to create air-filled pore space. In addition, the pH of the animal manure is raised to an approximate minimum of 9.5 to liberate endogenous gaseous ammonia in the air-filled pores for at least 1 hour, the level of gaseous ammonia being sufficient to reduce E. coli levels to less than 3.3*102 colony forming units/gram (dry weight) and Salmonella levels to less than 6.7*102 colony forming units/gram (dry weight), and to significantly reduce the levels of viruses and parasites. Subsequent to, or in conjunction with, this pathogen destruction, alkaline material and/or iron salts are added to the waste material to immobilize water-soluble pollutants. Such methods produce a granular, deodorized product suitable for use as a soil amendment.